1. Field of the Invention
The present invention provides a process for improving the color and the color stability of solutions containing C.sub.8-24 fatty alcohols and C.sub.8-24 alkyl polyglycosides by treating the solutions with alkali, maintaining the temperature of the treated solution for at least 2 hours, and finally distilling the treated solution to remove the fatty alcohol.
2. Discussion of the Background
Alkyl polyglycosides are non-toxic and easily degradable surfactants which are commonly used as detergents, cleaning agents, emulsifiers and dispersants. However, the desirable interfacial properties are only present if the alkyl groups of the polyglycosides have at least 8 C atoms.
Alkyl polyglycosides with long-chain alkyl groups are commonly prepared using one- or multi-step syntheses. For example, a two-step process is described in EP-A-0 306 652 which involves first glycosylating n-butanol and then transglycosylating the n-butyl glycoside with a long-chain alcohol. Unfortunately, after completion of the reaction, the alkyl polyglycoside product is present dissolved in the long-chain alcohol. To obtain a clear solution of the desired product, the long-chain alcohol must be removed.
A one-step preparation process is described, inter alia, in DE-A-4 101 252. Alternatively, EP-A-0 387 912 describes a one-step process in which long-chain fatty alcohols are first purified with alkali before they are reacted with glycosides under acidic catalysis. After neutralizing and distilling excess fatty alcohol from the reaction mixture, alkyl glycosides having improved color are obtained.
EP-A-0 132 046 describes a process in which an acidic reaction mixture containing glycosides and long-chain fatty alcohols is neutralized with an organic base, such as sodium methoxide, to a pH of 6.6 to 7. After distilling the fatty alcohol from the reaction mixture, alkyl glycosides having improved color are obtained.
Alkyl glycosides having long-chain alkyl groups can also be prepared in a one-step process as described in EP-A-0 362 671. After reacting a fatty alcohol with a glycoside, the reaction mixture is cooled to about 90.degree. C., adjusted with alkali to at least pH 8, preferably to pH 8 to 10. After 30 minutes, the fatty alcohols are distilled from the alkaline solution. After a final bleaching step, light-colored, color-stable alkyl glycosides are obtained. Unfortunately, alkyl polyglycosides obtained by this process still do not have completely satisfactory color. PG,4